Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate assembly 12. The planarizing machine 10 has a support table 14 with a top panel 16 at a workstation where an operative portion (A) of a polishing pad 40 is positioned. The top panel 16 is generally a rigid plate to provide a flat, solid surface to support the operative section of the polishing pad 40 during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the polishing pad 40 over the top panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. The supply roller 20 carries an unused or preoperative portion of the polishing pad 40, and the take-up roller 23 carries a used or post-operative portion of the polishing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the polishing pad 40 over the top panel 16 to hold the polishing pad 40 stationary during operation. A drive motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the polishing pad 40 across the top panel 16. As such, clean preoperative sections of the polishing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing the substrate assembly 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate assembly 12 during planarization. The carrier assembly 30 generally has a carrier head 31 with a plurality of vacuum holes 32 to pick up and release the substrate assembly 12 at appropriate stages of the planarizing cycle. A plurality of nozzles 41 attached to the carrier head 31 dispense a planarizing solution 42 onto a planarizing surface 43 of the polishing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the carrier head 31 via another shaft 39 such that the drive assembly 35 orbits the carrier head 31 about an axis B-B offset from a center point C-C of the substrate assembly 12.
The polishing pad 40 and the planarizing solution 42 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate assembly 12. The web-format planarizing machine 10 typically uses a fixed-abrasive polishing pad having a plurality of abrasive particles fixedly bonded to a suspension material. The planarizing solutions 42 used with fixed-abrasive pads are generally “clean solutions” without abrasive particles because the abrasive particles in conventional abrasive CMP slurries may ruin the abrasive surface of fixed-abrasive pads. In other applications, the polishing pad 40 may be a nonabrasive pad composed of a polymeric material (e.g., polyurethane), a resin, or other suitable materials without abrasive particles. The planarizing solutions 42 used with nonabrasive polishing pads are typically “abrasive” CMP slurries with abrasive particles.
To planarize the substrate assembly 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate assembly 12 against the planarizing surface 43 of the polishing pad 40 in the presence of the planarizing solution 42. The drive assembly 35 then orbits the carrier head 31 about the offset axis B-B to translate the substrate assembly 12 across the planarizing surface 43. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate assembly 12.
CMP processes should consistently and accurately produce, a uniformly planar surface on the substrate assembly 12 to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other components, many substrate assemblies develop large “step heights” that create a “topographical” surface across the substrate assembly 12. For the purposes of the present application, a “topographical” surface is a non-planar surface having high and low regions. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a highly planar surface at several stages of processing the substrate assembly 12 because even slightly topographical surfaces significantly increase the difficulty of forming submicron features. For example, it is difficult to accurately focus photo-patterns to within tolerances of 0.1 μM on topographical surfaces because submicron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes ate often used to transform a topographical surface into a highly uniform, planar surface.
In the competitive semiconductor industry, it is also highly desirable to produce such a uniformly planar surface at a desired endpoint on a substrate assembly. For example, when a conductive layer on the substrate assembly 12 is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly 12. Additionally, when a substrate assembly 12 is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should remove material until the desired endpoint is reached.
To accurately create highly planar substrate surfaces at the desired endpoint many CMP applications should initially remove material from high regions on topographical surfaces faster than low regions to change the topographical surface to a planar “blanket” surface. After creating a blanket surface on the substrate assembly, CMP applications should remove material from the blanket surface as quickly as possible without adversely affecting its planarity. The CMP processes should then stop removing material at the desired endpoint on the substrate assembly.
One problem with existing CMP techniques, however, is that it is difficult to selectively remove material from high regions on topographical surfaces without also removing significant amounts of material from low regions. It is also difficult to quickly remove material from a blanket substrate surface. For example, many existing CMP techniques that can selectively remove material from high regions on a topographical substrate surface are limited because they have very low polishing rates of the blanket surface. Such topographically selective CMP techniques are thus ineffective at expediently removing material from the blanket surface. Conversely, existing CMP techniques that have high polishing rates of blanket surfaces do not remove high regions on topographical surfaces without also removing material from low regions. Thus, existing CMP techniques generally do not provide both highly selective planarization of high regions on topographical surfaces and fast removal of material from blanket surfaces.
Another problem of CMP processing is that it is difficult to accurately stop planarization at the desired endpoint. One technique for accurately endpointing CMP processing is stop-on-feature (“SOF”) planarization in which a hard polish-stop layer of material having a relatively low polishing rate is formed on the substrate assembly so that the polish-stop layer has high points at the desired endpoint of the planarizing process. A softer cover layer of material having a higher polishing rate is then deposited over the polish-stop layer. The polish-stop layer resists planarization at the desired endpoint because the cover layer planarizes faster than exposed high points of the polish-stop layer. Even SOF planarizing techniques, however, may not accurately endpoint CMP processing because the difference in polishing rates between the cover layer and the polish-stop layer may cause “dishing” in the cover layer at contacts, damascene lines, shallow-trench-isolation structures, and other areas one the substrate surface where the cover layer dips below the exposed surfaces of the polish-stop layer. Thus, another problem of CMP processing is accurately stopping planarization at the desired endpoint.